Abstract:

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Microstructures developed by warm extrusion for Mg97Zn1Y2 alloy including long-period
stacking order (LPSO) phase have been investigated using SEM and TEM. The extruded magnesium
alloy with LPSO phase exhibits high strength and sufficient ductility. Such superior mechanical
properties appear by warm extrusion around the temperature of 623K. The microstructure of the
extruded alloy consists of matrix of fine-grained hcp phase and elongated grains with fine-lamellae
including LPSO phase. The grain size of hcp matrix was about 1μm, indicating that remarkable
grain refinement was occurred by extrusion since the grain size of as-cast alloy was about 500μm.
Special attention has been paid on the enrichment of solutes at stacking faults and grain boundaries
in the fine-grained matrix, which would contribute not only to the strengthening but also to the stability
of fine-grained structure because of its role of an inhibiter against grain coarsening.

Abstract: Warm compression tests of AZ31 Mg alloy were carried out at five temperatures in
30°C intervals from 210°C to 330°C. The samples of different thickness which were machined
from as-cast and pre-strained AZ31 billets were compressed into thickness 1mm and then cooled in
the air to room temperature. The microstructural evolution of AZ31 Mg alloy was investigated
during warm compression forming. The results show that all the samples have undergone a
microstructure changes to different scales in the range investigated. The twinning is the
predominant deformation mechanism for magnesium alloys at moderate temperatures and its
occurrence is dependent on temperature and strain. Microstructural evaluation indicates that the
mean size of the recrystallised grains decreases with increasing effective strain and temperature
because of sufficient dynamic recrystallization. The original grain has significant influence on
microstructural evolution during warm forming.

Abstract: The influence of plastic deformation and heat-treatment on the precipitation of Al3(Sc,
Zr) particles and the effect of these precipitates on hardening and softening processes of dilute
ternary Al-0.2wt.%Sc-0.1wt.%Zr alloy was investigated. Behaviour of two differently prepared
alloys (mold cast and prepared by powder metallurgy – PM) was investigated in as-prepared and in
cold rolled state. Both alloys exhibit the same peak age hardening, PM one reaches it already during
extrusion at 350°C. Both cold rolled alloys are highly resistant against recovery, which proceeds
without rapid hardness decrease at high temperatures. Evolution of hardness agrees well with that of
resistivity and with TEM observation.

Abstract: Rheocasting of alloys A206 and A201 was investigated in this study. Conical bars with
different silver contents were produced using CSIR rheoprocess technology, together with high
pressure die casting. The results showed that addition of Ag to alloy A206 increased the mechanical
properties of the alloy. However, the addition of Ag also resulted in Cu-rich phases to precipitate at
the grain boundaries of the as-cast material. The solution treatment used in this study was unable to
dissolve all of this phase, especially in the 1.12%Ag-containing alloy. This resulted in slightly
decreased mechanical properties compared to the 0.63%Ag-containing alloy. The T6 mechanical
properties (strength and elongation) obtained in this study for rheocast A206 and A201 are better
than those reported for permanent mould castings of alloy A206 and A201.

Abstract: A high Zn content Al-Zn-Mg-Cu alloy was prepared by spray forming process and the precipitate behavior and microstructure of the extruded alloy were also investigated. The precipitate sequence of the spray-formed alloy could be described as “α-solid solution → GPI zone → GPII zone (also called Metastable ′ )→ Stable  (MgZn2)” during artificial ageing treatment. In the early stage of artificial ageing treatment, the GPI zone was the main strengthening phase and kept coherent relationship with the matrix. With the increasing of ageing time, ′ phase dominate strengthening phase and kept semi-coherent relationship with the matrix. With the further increasing of ageing time,  phase took the place of ′ phase, and dominated the strengthening phase in the alloy. The grain size of the spray deposit is finer than that of cast alloys. The ultimate tensile strength of the alloy is over 810MPa in peak ageing condition.

Abstract: The effect of Cd and Sb addition on the microstructural and mechanical properties of as-cast AZ31 alloys was investigated and compared. The results indicate that the difference of Sb and Cd in the microstructure and mechanical properties of as-cast AZ31 magnesium alloy is significant. Addition of 0.15%Sb (mass fraction) to AZ31 alloy can refine the matrix and β-Mg17Al12 phase but not form a new phase Mg3Sb2. Oppositely, by addition of 0.3-0.7% Cd to AZ31 alloy, Cd was dissolved into the AZ31 alloy, the phase composition did not change but was refined also. Accordingly, the Cd-refined AZ31 alloy exhibits higher tensile and impact toughness and Brinell hardness properties than the Sb- refined one. The difference of Sb and Cd in the mechanical properties is possibly related to the solid solution of Cd into the matrix and formation of Mg3Sb2 which has the same close-packed hexagonal structure as α-Mg.